Adding API and unit testing for deferred canvas clearing/purging

REVIEW=http://codereview.appspot.com/5646057/
TEST=DeferredCanvas unit test



git-svn-id: http://skia.googlecode.com/svn/trunk@3181 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 19 insertions, 0 deletions

diff --git a/src/core/SkPictureRecord.cpp b/src/core/SkPictureRecord.cpp
index f31065b444..c56c104ebe 100644
--- a/src/core/SkPictureRecord.cpp
+++ b/src/core/SkPictureRecord.cpp
@@ -23,6 +23,7 @@ SkPictureRecord::SkPictureRecord(uint32_t flags) :
     fRestoreOffsetStack.push(0);
 
     fPathHeap = NULL;   // lazy allocate
+    fFirstSavedLayerIndex = kNoSavedLayerIndex;
 }
 
 SkPictureRecord::~SkPictureRecord() {
@@ -50,6 +51,10 @@ int SkPictureRecord::saveLayer(const SkRect* bounds, const SkPaint* paint,
 
     fRestoreOffsetStack.push(0);
 
+    if (kNoSavedLayerIndex == fFirstSavedLayerIndex) {
+        fFirstSavedLayerIndex = fRestoreOffsetStack.count();
+    }
+
     validate();
     /*  Don't actually call saveLayer, because that will try to allocate an
         offscreen device (potentially very big) which we don't actually need
@@ -60,6 +65,10 @@ int SkPictureRecord::saveLayer(const SkRect* bounds, const SkPaint* paint,
     return this->INHERITED::save(flags);
 }
 
+bool SkPictureRecord::isDrawingToLayer() const {
+    return fFirstSavedLayerIndex != kNoSavedLayerIndex;
+}
+
 void SkPictureRecord::restore() {
     // check for underflow
     if (fRestoreOffsetStack.count() == 0) {
@@ -74,6 +83,11 @@ void SkPictureRecord::restore() {
         offset = *peek;
         *peek = restoreOffset;
     }
+
+    if (fRestoreOffsetStack.count() == fFirstSavedLayerIndex) {
+        fFirstSavedLayerIndex = kNoSavedLayerIndex;
+    }
+
     fRestoreOffsetStack.pop();
 
     addDraw(RESTORE);
diff --git a/src/core/SkPictureRecord.h b/src/core/SkPictureRecord.h
index ff6585d375..e8fa370f9d 100644
--- a/src/core/SkPictureRecord.h
+++ b/src/core/SkPictureRecord.h
@@ -65,6 +65,7 @@ public:
                           const uint16_t indices[], int indexCount,
                               const SkPaint&) SK_OVERRIDE;
     virtual void drawData(const void*, size_t) SK_OVERRIDE;
+    virtual bool isDrawingToLayer() const SK_OVERRIDE;
 
     void addFontMetricsTopBottom(const SkPaint& paint, SkScalar minY, SkScalar maxY);
 
@@ -92,6 +93,10 @@ public:
 
 private:
     SkTDArray<uint32_t> fRestoreOffsetStack;
+    int fFirstSavedLayerIndex;
+    enum {
+        kNoSavedLayerIndex = -1
+    };
 
     void addDraw(DrawType drawType) {
 #ifdef SK_DEBUG_TRACE